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Date: Wed, 04 Sep 2013 07:42:10 -0400
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Subject: IVP pressurization
From: John Barrett <2thman1@gmail.com>
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Having trouble getting my pressurization to work effectively.
I did my best to seal the pressure vessel but never got above .25 PSID with m=
y 6 horse shop vac.  Used both pressure and vacuum to check for leaks.  No s=
moke but used a down feather and then a stethoscope with tympanic membrane r=
emoved.  Outflow valve is covered during these tests.

After lots of frustration i hired a guy who has built and/or pressurized abo=
ut a dozen IVPs to come take a look.  He determined using smoke that there w=
ere a couple of slight improvements to be made mostly in the wire bundles th=
rough the aft pressure bulkhead and after doing this he declared the vessel s=
eal very good. =20

So we deduced that maybe the shop vac is not as efficient at blowing air as I=
 thought, but my flying experience with the aircraft is that it doesn't do m=
uch better than the .25 PSID in flight up to 14.5K ft. =20

Wondering why there is inadequate pressurization with a good pressure vessel=
 leads to thoughts of outflow valve problems.  I bought the device with the k=
it in 1996 so it occurs to me the valve could be dirty or rubber diaphragm c=
ould be failing, etc.  I removed the outflow valve yesterday and tried to ex=
amine the parts.  i lubricated the mandrel that the poppet valve slides on w=
ith a very small spritz of LPS1 lubricant in case there was stiction there. =
 I did notice that with the poppet valve manually moved to the furthest clos=
ed position the diaphragm still had somewhere around a 1/32" gap at the seat=
ing perimeters.  Should the air pressure in flight fill that diaphragm to cl=
ose the gap or does this indicate the valve needs servicing?

Finally is there a way short of the manual dump switch to keep the system fr=
om pressurizing better than what I see by mismanaging the controller?  Am I j=
ust setting the pressurization up  wrong?  Have only been up to 3,000 ft ele=
vation airports, (KRDM) and lower - most at sea level.

Thanks for any help.

John Barrett

Sent from my iPad
=20=